In recent years, the trend in power or high speed motorboat design has been toward the establishment of high speed planing hulls as distinguished from slow, displacement hull designs. It has been found that in high speed planing hull designs, it is desirable and highly beneficial to place the mass of the engine in the rear of the hull above the planing surface. Placing the engine aft requires that a suitable drive train be provided between the engine at the rear of the boat to the forward, inboard end of the propeller shaft. To facilitate placement of the engine in the rear, the art has developed what has become known as marine V-drives. A marine V-drive enables the engine to be installed in the stern of the boat with the engine shaft line and the propeller shaft line intersecting in substantially an acute angle, at which point of intersection intermeshing transmission gears have been provided for the transmission of rotary motion from the engine to the vessel propeller.
However, there has long been a need in V-drive high-performance inboard planing-type speedboats for a better match of engine output to hull load and configuration, over the planing speed range. In this regard, the engine drive assembly is most critical. Prior marine drive train structures contain many deficiencies. For example, in most prior drive train structures, the propeller shaft extends through the hull at a considerable angle to the horizontal, with the result that substantial vertical forces are produced that tend to lift the boat, such vertical forces not contributing to the forward motion of the boat. Most speedboats incorporate step-down transmissions which are relatively inefficient for high performance marine device structures. If high-powered engines (such as for example, lower speed diesel engines) are used to achieve high boat speed, propeller stream cavitation makes it difficult, if not impossible, to accelerate the propellers to planing speeds when using step-up (or speed increase) marine transmissions.
Additionally, prior inboard motorboats have individual stern mounting constructions for the propeller shaft and for the steering (rudder) structure. There has long been a need for a simple, unitary, one-piece strut and stern steering support assembly that may be inexpensively manufactured and easily placed on the transom of an inboard motorboat.
When the boat is in sitting position in the water, its attitude or angle to the horizontal is relatively pronounced due to the weight concentration aft, such sitting position being referred to as the "in-the-hole-position". When power is applied and the boat slowly gets underway, difficulty is experienced in getting the boat "out-of-the-hole".
In a V-drive configuration, weight distribution dictates boat attitude. More weight aft results in more difficult and higher transition speed (displacement to planing), but higher top speed due to decreased wetted surface.
Controlled propeller cavitation provides two features:
1. Ability to accelerate surface-piercing, super-cavitating large blade area propellers in displacement mode; and
2. More efficient propulsion at high speeds by utilizing the energy of imploding air bubbles in conjunction with a surface-piercing, super-cavitating large blade area propeller.
Controlled cavitation enables the acceleration of the engines to their maximum output torque capability, thereby increasing the size and type of propeller to maximize top vessel speed.
Therefore, it is an object of the invention to provide a high-performance speedboat with a planing type hull incorporating a drive mechanism having at least one speed forward, step-up, V-gear hydraulic transmission with the propeller shaft extending rearwardly through the boat transom to provide a "thru-drive" system.
A further object of the invention is to provide a "thru-drive" system of the above type having a one-piece, unitary propeller strut and stern steering support assembly mounted on the boat transom capable of easy mounting, removal and replacement.
A further object of the invention is to provide a "thru-drive" power mechanism having a one-piece unitary propeller strut and stern steering support assembly of the above type which is capable of easy manufacture, assembly, maintenance, inspection and repair because of simplicity of structure.
A further object of the invention is to provide a "thru-drive" system of the above type incorporating means to control propeller cavitation and thus expeditiously bring the boat "out-of-the-hole" and up to cruising speed.
A further object of the invention is to provide a "thru-drive" system of the above type effecting a relatively flat propeller shaft angle when the boat reaches cruising speed whereby the propelling force upon the water is in a direction substantially parallel with the longitudinal axis of the boat.